The known waste disposal processes such as land fills, recycling, refuse incineration, and pyrolytic reaction do not provide a satisfactory solution to the growing refuse problems. The processes often contribute to and are an essential factor in destroying the environment.
Industrial product wrecks of composites, such as vehicles and household appliances, as well as oils, batteries, paints, varnishes, toxic slurries, medicaments and hospital waste are subject to strict, legally prescribed disposal regulations. However, domestic refuse is an uncontrolled, heterogenous mixture, which can contain virtually all types of special refuse fractions and organic constituents, whose disposal is in no way related to its harm to the environment.
Domestic refuse typically is stored inadequately in dumps from which digester gases and carbon dioxide escape in an uncontrolled manner into the atmosphere, and pollutant-containing liquids and eluates of the dumped waste pollute the ground water.
In order to reduce the treated refuse quantity it has already been proposed that the organic constituents of domestic refuse and sewage sludges be composted. However, this ignores the fact that these organic substances are heterogeneous and contain a large number of non-degradable toxic constituents such as chemicals, medicament and heavy metal residues, which remain in the compost and are returned to the biological cycle via plants and animals.
By recycling so-called valuable products an attempt is once again made to reduce the refuse quantity. However, this ignores the high costs involved in the separate collection and treatment of such waste and with repeated recycling the costs and prejudice to the environment increase, accompanied by a reduction in the usability of the products obtained.
In known refuse incineration plants the products for disposal pass through a broad temperature range up to approximately 1000.degree. C., at which mineral and metallic residual substances are not melted. The energy inherent in the remaining solids is not utilized. The short residence time of the refuse at higher temperatures and the large amount of dust produced by blowing in large quantities of nitrogen-rich combustion air into the uncompressed disposal products favor the dangerous formation of chlorinated hydrocarbons. Therefore the waste gases from refuse incineration plants undergo afterburning at higher temperature. In order to justify the high costs involved in such plants, the abrasive and corrosive hot gases with their high dust quantities are passed through heat exchangers. During the relatively long residence time in the heat exchanger chlorinated hydrocarbons are once again produced through denovo synthesis, which chlorinated hydrocarbons combine with the entrained dust and lead to highly toxic filtrates. It is scarcely possible to estimate the resulting damage and the costs involved in their elimination.
Despite the high technical expenditure of the prior art, after combusion approximately 40% of the refuse to be disposed of is left behind in the form of ash, slag and highly toxic filtrates, whose dangerousness level can be compared with that of radioactive waste and which must be disposed of in cost-intensive manner. In order to reduce the volume to be dumped, it is known to separate the metallic components from the residual substances and supply them for separate use. The remaining ash and slag undergo a high temperature melting process which involves high energy costs. As a result of the heterogeneous starting substances to be melted, the slag is inhomogeneous and contains considerable proportions of organic residual substance particles which, surrounded by the liquid melt, are not oxidized.
As a result of shock-like cooling of the melt in a water bath a heterogeneous melt granular material is obtained, which shatters in uncontrolled manner at its thermal breakage points, so that the enclosed pollutants can be eluted again. A high energy expenditure of hitherto approximately 200 litres of fuel oil per tonne of melt remains unused, because the thus obtained melt granular material can only be employed as a filler in road building and the like.
In conventional reactors the hitherto used pyrolysis processes have a wide temperature spectrum similar to refuse incineration. High temperatures prevail in the gasification zone. The hot gases which form are used for preheating the not yet pyrolyzed disposal material, cool and pass through the temperature range relevant for the formation of chlorinated hydrocarbons and which therefore represents a hazard.
All known pyrolysis processes for unsorted, unbound and drained disposal products do not provide an adequately gas-permeable bed, require excessive energy costs in the case of inadequate gas production and also long residence times in the reactor. As a result of the heat flow and the internal gas pressure there are large amounts of dust produced which consequently require large filter capacities. If water gas is to be produced, then it is necessary to add separately produced superheated steam, i.e. extraneous steam to the gasification zone. The remaining solids are generally not melted and must instead be supplied to separate disposal and can therefore be compared with a conventional refuse incineration plant.
In order to produce ecologically unobjectionable, usable pure gas, the pyrolysis gases generally pass through a cracker prior to purification. By using a heat exchanger, it is also known to utilize the thermal energy inherent in the hot gases. However, as a result of the residence time of the gases in the heat exchanger chlorinated hydrocarbons form, which are released during the thermal utilization of the gas obtained.
When using shaft furnaces for refuse incineration, inter alia the important disadvantage of sticking together and bridge formation of the disposal products to be pyrolyzed in the furnace occurs, so that it is necessary to equip such reactors with mechanical aids, such as poking bars, vibrators and the like, without providing a satisfactory solution for the problem.
Revolving tube and fluid bed gasifiers, due to the mechanical abrasion on the furnace wall as a result of the in part sharp-edged disposal products, lead to long shutdown times, extremely high dust formation and require technically complicated, gas-tight locks. This leads to a large amount of maintenance with the correspondingly high costs.
To avoid the disadvantages of the above-described refuse incineration and pyrolysis processes, it is also known to decompose waste and toxic substances by means of a mineral or metallic high temperature melting or molten bath, or to feed the waste into the latter, so as in this way to ensure a rapid Pyrolytic decomposition of the disposal products at high temperatures. The essential disadvantage of such a procedure is that a utilization of the liquid and/or wet waste is impossible due to the explosion-like deflagration risk and as a result of the high pressures which occur from the gases which form which do not have an adequately long residence time in the melt in order to reliably destroy organic pollutants. In the case of dried, non-degassed organic waste the gas pressure through the decomposing organic products is too high to ensure an adequately long residence time. After a short time the melt products are saturated with non-oxidizable carbon particles enveloped by melt liquid, so that it is not appropriate to supply further disposal products.
In another known thermal process for refuse disposal initially mineral and metallic products are separated from organic constituents, the separated organic constituents are dried and then pulverized. The powder obtained is introduced into a high temperature molten bath or a combusion chamber having an appropriate temperature and by blowing in oxygen or oxygen-enriched air is immediately decomposed and the pollutants are destroyed.
Although from the ecological standpoint this process leads to satisfactory results, it still has significant disadvantages. Thus, e.g. no liquid waste and disposal products can be disposed of in combined structures and the resulting costs are un-acceptable.
The previously described combusion and pyrolysis processes jointly suffer from the disadvantage that the liquids or solids evaporated during combusion or pyrolytic decomposition are mixed and led off with combusion or pyrolysis gases before they have reached the temperature and residence time in the reactor necessary for destroying all pollutants. The evaporated water is not made usable for water gas formation. Thus, generally, after-burning chambers are provided in refuse incineration plants, and crackers are provided in pyrolysis plants.
The present invention aims at providing a process of the aforementioned type, which the aforementioned disadvantages are obviated in the case of random disposal products, so that there is no harm to the environment and simultaneously it is possible to obtain high-grade, widely usable and semifinished or finished industrial products from the residual materials, while minimizing the technical expenditure and process costs necessary for this.